Formulations that include fibers in powder coated primer or topcoat layers have been suggested in the art for providing chip resistance on steel substrates at elevated temperatures, or as non-skid coatings. See for instance U.S. Pat. No. 6,861,467; US 2002/0110682; US 2010/0297422; and US 2011/0184110.
U.S. Pat. No. 5,624,735 describes sheet molded compound articles formed of fiber reinforced compression molded thermoset polymer which have a machined edge. The machined edge and the bordering margin are degassed and then coated with a cured coalesced powder coating primer that tapers from the machined edge on the boarding margin to a primerless exterior surface. The primed edge minimizes surface defects in a subsequently applied top coat that are attributed to trapped gasses in the SMC article. This edge coating is said to provide improved finish results relative to an alternative priming technique described in U.S. Pat. No. 5,021,297 that applies primer to the entire exterior. There is no suggestion to use fiber in the edge primer.
In the field of Archery, use of fiber reinforced thermoset composite components in compound bows is well established. Typically such bows include a riser and flexible limbs formed from the composite that are attached to the riser. The riser may be made of metal or composite. These polymer matrix composites typically use unidirectional fibers in alignment with the bending axis of the arm. In many cases they must be machined after lay-up, at least the compression side of the arm to provide arms in a range of bending strengths and/or lengths to meet the requirements of different customers.
Since the 1970's a number of powder paints have been used to successfully coat both metal and composite archery bow components and provide an exceptionally durable and somewhat stronger finish as compared to liquid system finishes. Most successful are epoxy based powder painting systems, as they appeared to have better bonding to the substrates and more durability than did the polyester based powder systems when used in our application.
From experience at the time, it was learned that some composite bow limbs when coated with the epoxy powder paint exhibited substantially increased fatigue resistance testing as compared to the same composite bow limbs that had been coated with conventional liquid system paints. The bow limbs that benefited the most from the epoxy powder coating process were those that had gel coat machined from the outer layer of the composite material which resulted in exposing some of the reinforcement filaments on the outer surfaces of the limbs. This occurred when a bow limb billet composed of unidirectional reinforcement filaments was ground into to provide a desired shape and bending characteristic for a given bow limb design. Even though care was taken to limit the shaping of the bow limb and the cutting of the reinforcement fibers to the compressive side of the limb the result was still that a considerable number of the fibers/filaments become exposed. The addition of the epoxy power coating to the limb effectively applied a well bonded protective layer over these fibers somewhat similar to the original epoxy gel coat sufficiently sealing the cut filament ends.
Single and double powder coating of ground to shape composite billets provided a durable product for the loads that were being applied to composite bow limbs for a number of years. However, the bow limbs being used on some of today's bows are being exposed to even higher demands in use and reliability. Consequently there exists a need to further improve the fatigue durability of machined composite bow limbs.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.